N. D. Kuzmichev

The analytic properties and symmetry of YBa2Cu3O7−K polycrystals magnetization curves obtained from experimental harmonics spectrum of response signal for 500 Oe amplitude modulation

Abstract Using the Taylor series for Fourier components the experimental spectrum of response signal emf of YBa 2 Cu 3 O 7−K polycrystals obtained for ac magnetic field 500 Oe ranging from 0 to about 1000 Oe was analyzed. The analytic dependence of initial magnetization curve of YBa 2 Cu 3 O 7−K polycristals was restored from this spectrum. The applicability of critical state model for description of restoration magnetization are discussed.

The modulated investigates of the YBa2Cu3O7−x single crystals I–V characteristics nonlinearity near Tc

Abstract Temperature and d.c. magnetic field dependences of the YBa2Cu3O7−x single crystals I–V characteristics near Tc has been investigated with the help of modulation method. 11 harmonics were studied. It was found that the temperature dependences of all harmonics have the maximum at the temeraure 92.0 K. I–V characteristics of the single crystals were reconstructed with the help of harmonics behavior analysis. Comparison of d.c. and the reconstructing of the I–V characteristics showed their good agreement. A model of the I–V characteristics on the base of Kosterlitz-Thouless(KT) transition is proposed.

The modulated research of YBa2Cu3O7−x single crystals and ceramics magnetization

Abstract In this work experimental modulated research of magnetization of YBa2Cu3O7−x single crystals and ceramics was analyzed. The dependences of harmonic amplitudes of magnetization at a.c. magnetic field 5

Detection of YBa2Cu3O7−x magnetization nonlinearity in a pseudogap region

The temperature dependences of magnetization higher harmonics were studied experimentally in single-domain YBa2Cu3O7−x samples above Tc. YBa2Cu3O7−x magnetization nonlinearity was found in different samples up to temperatures T = 103–112 K, which is much higher than the temperature of transition into the superconducting state of the given compound. The observed specific feature of YBa2Cu3O7−x magnetization is associated with the occurrence of pseudogap state in this compound.

New experimental criterion of the Berezinskii-Kosterlitz-Thouless transition

Based on the experimental study of YBa2Cu3O7−x single crystal nonlinearity near Tc, a new criterion for observing the Berezinskii-Kosterlitz-Thouless (BKT) transition in cuprate HTSC compounds was proposed. The criterion consists in the existence of the maximum in the dependence of the voltage of the second harmonic of the sample response signal excited by alternating current on the direct bias current. It was shown that the position of the second harmonic maximum is independent of temperatures near Tc, which is consistent with the BKT transition independence of the measuring current.